﻿#define  _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
int main()
{
	int qs = 20;
	int kp = qs;
	while (kp >= 2)
	{
		qs += kp / 2;
		kp = kp / 2 + kp % 2;
	}
	printf("%d", qs);

	return 0;
}